Surface Effect on Ions Distributions in Nanoporous Media, a Molecular Dynamics Study

Abstract

Nanopore scale surface has become widely recognized as an important transport parameter. Understanding ions transport by a fundamental approach based on the mesoscopic and macroscopic physics of fluids is only partial at this level of description. In this paper, we go beyond the theoretical approach by performing classical Molecular Dynamics (MD) with polarizable force fields for water and ions, a method particularly well adapted to the nanoscale. The aim of this work is to better understand the physical phenomena involved in nano-confined aqueous solutions, especially the role of "solute-solute" and "solute-interface" interactions within nanopore. We have simulated ions transport through a 1 nm internal radius, rigid and neutral atomistic nanotube connected with two reservoirs. The study focused on water/nanopore interface, more particularly on its effects due to the nature of the nanopore surface hydrophobic/hydrophilic. Also, we study the distribution of the ions and water molecules. The simulations illustrated that the surface has a major effect on the ions distribution in aqueous solutions near interfaces and in nanopore, the I- anions prefer to localize towards the center of hydrophilic pore surface, while  this anions prefer to localize at the interface in hydrophobic pore surface. The ions distributions can be explained by the efficacy role of the water structure, the ion size and polarizability. These results provide useful information for predicting properties of nanoporous membranes, and give a guide to designing synthetic membranes for applications in nanofiltration, etc.
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